Implantable stimulation devices are devices that generate and deliver electrical stimuli to body nerves and tissues for the therapy of various biological disorders, such as pacemakers to treat cardiac arrhythmia, defibrillators to treat cardiac fibrillation, cochlear stimulators to treat deafness, retinal stimulators to treat blindness, muscle stimulators to produce coordinated limb movement, spinal cord stimulators to treat chronic pain, cortical and deep brain stimulators to treat motor and psychological disorders, and other neural stimulators to treat urinary incontinence, sleep apnea, shoulder sublaxation, etc. The present invention may find applicability in all such applications, although the description that follows will generally focus on the use of the invention within a Spinal Cord Stimulation (SCS) system, such as that disclosed in U.S. Pat. No. 6,516,227, which is incorporated herein by reference in its entirety.
Spinal cord stimulation is a well-accepted clinical method for reducing pain in certain populations of patients. As shown in FIGS. 1A and 1B, a SCS system typically includes an Implantable Pulse Generator (IPG) 100, which includes a biocompatible case 30 formed of titanium for example. The case 30 typically holds the circuitry and power source or battery necessary for the IPG to function, although IPGs can also be powered via external RF energy and without a battery. The IPG 100 is coupled to electrodes 106 via one or more electrode leads (two such leads 102 and 104 are shown), such that the electrodes 106 form an electrode array 110. The electrodes 106 are carried on a flexible body 108, which also houses the individual signal wires 112 and 114 coupled to each electrode. In the illustrated embodiment, there are eight electrodes on lead 102, labeled E1-E8, and eight electrodes on lead 104, labeled E9-E16, although the number of leads and electrodes is application specific and therefore can vary.
Portions of an IPG system are shown in FIG. 2 in cross section, and include the IPG 100 and an external controller 12. The IPG 100 typically includes an electronic substrate assembly 14 including a printed circuit board (PCB) 16, along with various electronic components 20, such as microprocessors, integrated circuits, and capacitors mounted to the PCB 16. Two coils are generally present in the IPG 100: a telemetry coil 13 used to transmit/receive data to/from the external controller 12; and a charging coil 18 for charging or recharging the IPG's power source or battery 26 using an external charger (not shown). The telemetry coil 13 can be mounted within the header connector 36 as shown.
As just noted, an external controller 12, such as a hand-held programmer or a clinician's programmer, is used to wirelessly send data to and receive data from the IPG 100. For example, the external controller 12 can send programming data to the IPG 100 to set the therapy the IPG 100 will provide to the patient. Also, the external controller 12 can act as a receiver of data from the IPG 100, such as various data reporting on the IPG's status.
The communication of data to and from the external controller 12 occurs via magnetic inductive coupling. When data is to be sent from the external controller 12 to the IPG 100, coil 17 is energized with an alternating current (AC). Such energizing of the coil 17 to transfer data can occur using a Frequency Shift Keying (FSK) protocol for example, such as disclosed in U.S. patent application Ser. No. 11/780,369, filed Jul. 19, 2007, which is incorporated herein by reference in its entirety. Energizing the coil 17 induces an electromagnetic field, which in turn induces a current in the IPG's telemetry coil 13, which current can then be demodulated to recover the original data. Such data is typically communicated at a frequency of about 125 kHz, which in an FSK protocol might be 121 kHz for a logical ‘0’ and 129 kHz for a logical ‘1’. As is well known, inductive transmission of data occurs transcutaneously, i.e., through the patient's tissue 25, making it particularly useful in a medical implantable device system.
A typical external controller 12 is shown in further detail in FIGS. 3 and 4A-4C. FIG. 3 shows a plan view of the external controller, including its user interface. The user interface generally allows the user to telemeter data (such as a new therapy program) from the external controller 12 to the IPG 100 or to monitor various forms of status feedback from the IPG for example. The user interface is somewhat similar to a cell phone or to other external controllers used in the art, and includes typical features such as a display 265, an enter or select button 270, and menu navigation buttons 272. Soft keys 278 can be used to select various functions, which functions will vary depending on the status of the menu options available at any given time. A speaker is also included within the housing 215 to provide audio cues to the user (not shown). Alternative, a vibration motor can provide feedback for users with hearing impairments.
FIGS. 4A-4C show various views of the external controller 12 with its outer housing 215 removed. Visible on the underside of the main printed circuit board (PCB) 120 is a battery 126 that provides power to the external controller 12. The battery 126 may be rechargeable via a power port 280 (FIG. 3) coupleable AC power source 292 (e.g., a wall plug), or may comprise a non-rechargeable battery. If the external controller 12 contains no battery 126, power port 280 would be used as the exclusive means for powering the device. A data port 282 (FIG. 3) is provided to allow the external controller 210 to communicate with other devices such as a computer 295. Such a data port 282 is useful for example to share data with another machine, to allow the external controller 210 to receive software updates, or to allow the external programmer 210 to receive a starter therapy program from a clinician programmer. An unlock button 281, recessed into the side of the housing, can be used to unlock the keys and buttons, and can be activated by pressing and holding that button for some duration of time (e.g., one second).
As alluded to earlier, FIGS. 4A-4C show the electronics within the housing 215 of the external controller 12. As can be seen from the various views, the electronics are generally supported by PCB 120. In the illustrated example, the front of the PCB 120 (FIG. 4A) includes the display 265 and the switches 122 which interact with the various buttons present on the housing 215 (see FIG. 3). The back of the PCB (FIG. 4B) includes the battery 126 and the data coil 17. In this embodiment, the back contains much of the circuitry (e.g., integrated circuits, capacitors, resistors, etc.) necessary for the external controller 12 to function. For example, the external controller 12's main microcontroller would reside on the back side of the PCB 120. However, this in not strictly necessary, and circuitry could also appear on the front of the PCB 120 or elsewhere.
Of particular concern to manufacturers of external controllers 12 is the data coil 17. As one skilled in the art will appreciate, the coil 17 is generally difficult and expensive to manufacture. Coils 17 are typically formed out of insulated strands of solid or stranded copper wire. Such wire is wound around a preformed shaped called a mandril to form the coil 17. It is important to precisely wind the coil 17 with the correct number of turns, such that the correct resistance and inductance of the coil is achieved. Once wound, the coil 17 is then typically bonded together with an adhesive to prevent it from unraveling. Depending on the type of insulation used, solvent or heat application can also assist in the bonding of the wires. The end terminals of the wire then must be stripped to verify inductance and resistance, and to check for shorted turns resulting from damage to the wire's insulation during winding. The finished coil is then attached to the PCB 120 with adhesive, and the terminals soldered to the PCB. If necessary, the coil 17 may require special mounting structure to elevate the coil above the underlying circuitry on the PCB 120, as best shown in the side view of FIG. 4C. Even if successfully manufactured and mounted to the PCB 120, the coil 17 remains a reliability concern, due to its susceptibility to mechanical shock, vibration, temperature fluctuations, and/or humidity. Additionally, the sheer bulk of the coil 17 adds to the overall size of the external controller 12, which is not desirable. This disclosure provides embodiments of a solution to mitigate shortcoming related to the manufacturing and reliability of the communication coil in the external controller.